1. Field of the Invention
The invention relates to electric motors and is directed more particularly to an electric motor having in an endframe portion thereof a brush retainer.
2. Description of the Prior Art
In electric motors, brushes are commonly retained in brush tubes which usually are molded integrally with a plastic endframe portion of the motor. The endframe and brush tubes typically are of a plastic material. The brush tubes are square in cross-section and hollow, somewhat like elevator shafts, in which spring-biased brushes are slidably movable into engagement with the commutator of the motor.
In assembly of such motors, it is common that a coil spring is inserted in a brush tube and, thereafter, a brush, with a shunt attached thereto, is inserted in the brush tube on top of the spring. In shipment and handling prior to assembly, it is sometimes the case that the brush and spring fall out of the open end of the tube. At the final assembly point, the brush and spring must be reinserted and properly positioned in the brush tube. It is on occasion overlooked that the spring is missing. It is usually apparent when the brush is missing, but sometimes the brush is replaced without the absence of the spring having been noticed. In some instances, the shunt will, for a limited time, exercise spring-like properties and hold the brush in a commutator-engaging position. However, the shunt usually cannot maintain its spring-like performance and, in due course, the brush falls away from commutator engagement, terminating proper operation of the motor.
Accordingly, at best, replacement of a missing brush, or both brush and spring, occasions delay in the assembly process, and, at worst, can result in assembly of a faulty motor. There is then, a need for a brush retainer which prevents loss of brushes and brush springs from brush tubes.
When the brushes remain in their proper positions, they still occasion time delays at the assembly point. The brushes, which are under spring pressure urging them toward the open ends of their brush tubes, typically extend beyond the open ends of the brush tubes and must be urged back into the brush tubes fully to allow a commutator to assume its rightful position in the endframe. Operators usually use plier-like tools to spread the brushes apart, to permit insertion of the commutator. Once the commutator is in place, the plier-like tool is removed, allowing the brushes to snap into engagement with the commutator.
In the endframe there is provided means for retaining a bearing which, in turn, retains a portion of the drive shaft of the motor. A face of the bearing, which usually is of metal, receives a metal face of the commutator. In operation, the commutator face moves rotatably against the bearing face and generates noise. In some applications, it is desirable that the motor operate as quietly as possible. For example, in motors for operating automobile power seats, it is necessary that the motor run quietly so as not to introduce irritating noises into the automobile passenger compartment.
Thus, there is a need for means to substantially reduce the noise generated at the commutator-bearing interface.